A stroke (also called a cerebrovascular accident) occurs when brain tissue is deprived of its blood supply. A stroke is the equivalent of a heart attack, but in the brain. Strokes can result from a blockage of blood flow to the brain (called an ischemic stroke) or from a ruptured blood vessel that bleeds into the brain (called a hemorrhagic stroke). Damage to the brain from a stroke begins within seconds of the interruption in blood flow.
About 80 percent of all strokes are ischemic strokes that result from a blockage in a blood vessel in the neck or the brain. Ischemic strokes can cause severe disability. There are three ways that blood flow can be blocked in an artery leading to the brain: when a clot forms inside the blood vessel (called cerebral thrombosis), when a clot travels from another part of the body and becomes lodged in a blood vessel (called cerebral embolism), or when an artery becomes severely narrowed (called stenosis).
Hemorrhagic strokes can result from rupture of an aneurysm (a weak, thin blood vessel wall); from changes in small arteries resulting from high blood pressure or diabetes; or, less commonly, from an arteriovenous malformation (see "Other Neurological Disorders," page 341). When the bleeding occurs within the brain itself, the stroke is classified as an intracerebral hemorrhage. If the bleeding occurs within the membranes between the brain and the skull, it is called a subarachnoid hemorrhage.
Sometimes blood flow to the brain is diminished or blocked for just a few minutes. This temporary cutoff of blood is called a transient ischemic attack (TIA). The symptoms of a TIA clear up quickly. Just as angina indicates an increased risk for heart attack, a TIA is a warning sign for a future stroke. Familiarize yourself with the following warning signs of stroke.
Symptoms of a stroke often appear suddenly, without warning. If you have one or more of the following symptoms, call your doctor, 911, or your local emergency number immediately. The sooner you get treatment for a stroke, the more likely you are to recover. These symptoms may be accompanied by drowsiness, nausea, or vomiting.
• sudden numbness or weakness in your face, an arm or a leg, or on one side of your body
• sudden confusion or difficulty speaking or understanding speech
• sudden difficulty with vision (such as dimness or double vision) in one or both eyes
• sudden difficulty walking, dizziness, or loss of balance or coordination
• sudden severe headache with no obvious cause
A stroke can occur in anyone at any age. However, the following factors can increase your risk of having a stroke:
• High blood pressure is the leading risk factor for stroke. If your blood pressure is high (more than 140/90), work with your doctor to lower it (see page 217). High blood pressure in blood vessels in the brain can cause them to rupture. It also can cause blood vessels to narrow by thickening their walls. Obstructions such as blood clots and tiny pieces of fatty plaque may lodge in blood vessels that supply blood to the brain.
• Smoking has been linked to the buildup of fatty deposits in the walls of the carotid arteries, the main arteries in the neck that supply blood to the brain. Blockage of these arteries is a leading cause of stroke in white Americans. In addition, smoking raises blood pressure, reduces the amount of oxygen in the blood, and makes blood thicker and more likely to clot. (For information on quitting smoking, see page 107.)
• Heart disease can produce blood clots that may break loose and block blood vessels in or leading to the brain. Preventing or treating heart disease can reduce the risk of developing blood clots.
• Prior TIAs or strokes indicate that a problem exists in the blood vessels supplying the brain. Contact your doctor as soon as possible if you think you have had a TIA. Carefully following your doctor's advice will reduce your risk for stroke.
• Diabetes (see page 365) increases fatty deposits inside blood vessels throughout the body, including the brain. If blood glucose levels are high at the time of a stroke, the damage to the brain can be severe. Keeping diabetes under control will help reduce the risk of stroke.
If you have one or more of the above disorders or conditions, work closely with your doctor to reduce your risk for stroke. If you smoke, the sooner you quit, the sooner your risk for stroke will begin to decline. Most people at risk for stroke are advised by their doctors to take anticoagulants (blood thinners) such as warfarin, or platelet inhibitors (drugs that discourage formation of blood clots) such as aspirin, clopidogrel, or ticlopidine.
If the arteries that supply blood to your brain—the carotid arteries—are narrowed, your doctor may recommend a carotid endarterectomy (a surgical procedure to remove fatty deposits from the walls of the carotid arteries). Before surgery, your carotid arteries will be examined for blockages using a procedure called cerebral angiography (see "Diagnostic Procedures," page 342). In people who have significant narrowing of the carotid arteries that has caused a stroke or TIAs and who are at low risk for complications, carotid endarterectomy can significantly reduce the risk of stroke.
The severity of a stroke may range from mild to disabling to life-threatening, depending on the type of stroke and its location in the brain, the amount of tissue affected, and the amount of time that passes before treatment begins. Because each side of the brain controls the opposite side of the body, a stroke in the left side of the brain affects the right side of the body, and a stroke in the right side of the brain affects the left side of the body. Strokes in areas of the brain that carry out specific functions (such as speech, sight, or memory) will interfere with or possibly eliminate that ability. Strokes in vital brain structures can result in coma or even death. In a hemorrhagic stroke, bleeding from a ruptured artery can irritate other blood vessels in the brain, causing them to go into spasm and damage adjacent brain tissue.
The amount of damage caused by a stroke is directly related to promptness of treatment. Ideally, treatment should begin during the stroke. If injected within 3 hours of the onset of symptoms, a thrombolytic (clot-dissolving) drug such as tissue plasminogen activator (tPA) can greatly reduce long-term damage from an ischemic stroke. When contacting emergency medical personnel, be sure to tell them that you (or a family member or friend) have symptoms of a stroke.
For hemorrhagic strokes, doctors bring blood pressure under control, if necessary. In some cases blood may be drained to reduce pressure on surviving brain tissue and prevent further damage. The person may need to undergo surgery to repair a bleeding artery or to remove blood clots.
When blockages or other types of damage occur in small blood vessels in the brain, they may gradually destroy brain tissue in many areas. Over time, symptoms of dementia may develop, including confusion, loss of short-term memory, getting lost in familiar places, bladder or bowel incontinence, emotional disturbances, difficulty following instructions, or difficulty handling money. Symptoms usually begin after age 60.
Brain and Nervous System
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